This application makes reference to and claims all the benefits accruing under 35 U.S.C. Section 119 from an application entitled xe2x80x9cAvalanche Photodiodexe2x80x9d filed with the Korean Industrial Property Office on Sep. 26, 2001 and there duly assigned Serial No. 2001-59499.
1. Field of the Invention
The present invention generally relates to a technique of manufacturing a photodiode, and more particularly to an avalanche photodiode.
2. Description of the Related Art
In general, an avalanche photodiode is used for converting an input optical signal to an electrical signal, while amplifying the input signal through the avalanche effect by the injection of carriers into an area applied with a high electrical field. The avalanche photodiodes typically include a planar-type avalanche photodiode and a mesa-type avalanche photodiode, both of which have a common structure of a multiplicity of stacked layers with an amplifying layer and an absorbing layer on a semiconductor substrate. The planar avalanche photodiode, however, inherently has some degree of curvature at the edge portion of a p-n junction semiconductor, causing an electrical field in the edge portion to become higher when subject to the same bias voltage. The result is a gain in the spatial difference. Meanwhile, the mesa-type avalanche photodiode also has some advantage in achieving a spatially uniform electrical field. However, it still has disadvantages in that the surface leakage current is induced in the absorbing layers with a small band gap, thereby degrading reliability during operation.
The present invention has been proposed to solve the foregoing problems of the related art. Accordingly, the present invention is directed to an avalanche photodiode that is capable of generating a minimal surface leakage current as well as achieving a uniform electrical field.
According to an aspect of the present invention, there is provided an avalanche photodiode, which includes a semiconductor substrate with a lower electrode underneath the substrate; an amplification layer producing pairs of electron-holes through ionized collision of carriers injected by an internal electrical field; and, an absorption layer producing the carriers in accordance with splitting of the pairs of electron-holes by the internal electrical field, wherein the pairs of electron-holes are excited by an incident light ray. The avalanche photodiode further includes a contact layer formed on the absorption layer, having a core section in the center of the contact layer and a guard section surrounding the core section, spaced apart from each other; and, at least one upper electrode comprising at least one core electrode formed on the core section and at least one guard electrode formed on the guard section. The upper electrode generates the internal electrical field together with the lower electrode.
Preferably, the avalanche photodiode further includes a charge layer formed between the amplification layer and the absorption layer in order to apply relatively low intensity or high intensity of electrical field respectively to the absorption layer and the amplification layer.
Preferably, the avalanche photodiode may further include a grading layer formed between the amplification layer and the absorption layer in order to inject the carriers into the amplification layer efficiently.
Preferably, the avalanche photodiode may further include an insulation layer deposited on an exposed surface of the amplification layer and the contact layer so as to insulate and protect the exposed surface of the amplification layer and the contact layer.
More preferably, the insulation layer may be made of a transparent material, so as to transmit a light ray incident on the avalanche photodiode inwardly.